ORNL-2106 - the Molten Salt Energy Technologies Web Site

couples were used on this loop to eliminate the
severe oxidation that occurred in previous loop
assemblies where the Chromel-Alumel thermocouple
leads passed through heaters. The change in
thermocouple materials necessitated a redetermi-
nation of thermocouple corrections.
Three conditions contributing to errors in temper-
ature measurement were investigated for the
platinum-platinum-rhodium thermocouples used.
First, the thermoelectric output of the couples
might be changed because of incompatibility with
Inconel; second, the junction of the thermocouple
is cooler than the lnconel surface to which it is
attached because of air cooling; third, the outside
surface of the inconel is cooler than the surface
in contact with fuel because of the heat flux
through the wall.
A compatibility test was run in which the plati-
num-pl ati num-rhod i um thermoco up I c s were we I ded
to lnconel and heated for 1000 hr at 9000C. The
thermocouples were found to be mechanically
sound after this treatment, and their absolute
calibration has changed not more than 1.2OC.
Tests were also run to determine the temperature
correction necessary because of air cooling of the
thermocouple bead. A segment of the loop was
mocked up in full scale, with electrical heating
PERIOD ENDING JUNE 10, 1956
instead of fission heating, and the thermocouples
were mounted on the fuel tube in the same way
that they are mounted on the loop. Surface temper-
atures were observed, with an optical pyrometer,
through a quartz window and compared with the
thermocouple readings. These tests were similar
to those reported previously, lo which yielded
different results for different thermocouple ma-
terials. The differences are no doubt due to bead
geometry differences that result from melting-point
differences during thermocouple fabrication. The
results of these tests are shown for six thermo-
couple assemblies in Fig. 4.2.11. For the oper-
ating conditions of the LITR vertical in-pile loop
the correction amounts to 15 f 10%.
The correction for the differential temperature
through the wall of the loop was calculated by
using theoretical heat transfer relationships in
the loop and experimental flux data obtained from
previous loop operation in the LITR.” The heat
’OW. E. Browning, G. W. Keilholtz, and H. L.
Hem hill ANP Quar. Ptog. Rep. Match 10. 1955,
ORdL-ld64, .- p 146.
“G. W. Keilholtz et ai., ANP Qua~. Prog. Rep.
Sept. lo, 1955, ORNL-1947, p 164.
UNCLASSIFIED
ORNL-LR- DWG 44746
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